IEEE 802.11 Services
IEEE 802.11 defines a number of services that need to be provided by the wireless LAN to provide functionality equivalent to that which is inherent to wired LANs. These are the most important services:
Association. Establishes an initial association between a station and an access point. Before a station can transmit or receive frames on a wireless LAN, its identity and address must be known. For this purpose, a station must establish an association with an access point. The access point can then communicate this information to other access points to facilitate routing and delivery of addressed frames.
Reassociation. Enables an established association to be transferred from one access point to another, allowing a mobile station to move.
Disassociation. A notification from either a station or an access point that an existing association is terminated. A station should give this notification before leaving an area or shutting down. However, the MAC management facility protects itself against stations that disappear without notification.
Authentication. Used to establish the identity of stations to each other. In a wired LAN, it's generally assumed that access to a physical connection conveys authority to connect to the LAN. This is not a valid assumption for a wireless LAN, in which connectivity is achieved simply by having an attached antenna that's properly tuned. The authentication service is used by stations to establish their identity for stations with which they want to communicate. The standard doesn't mandate any particular authentication scheme, which could range from relatively unsecure handshaking to public-key encryption schemes.
Privacy. Used to prevent the contents of messages from being read by anyone other than the intended recipient. The standard provides for the optional use of encryption to assure privacy.